Cardiovascular disease (CVD) is a major cause of death among End Stage Renal Disease (ESRD) patients. CVD is caused in part by endothelial dysfunction. Three metabolic pathways have a major role in the regulation of endothelial function: the L-arginine-Nitric Oxide (NO) pathway, the methionine-homocysteine cycle and the asymmetric dimethylarginine (ADMA). This application is a comprehensive study, aimed at integrating metabolic, nutritional, physiologic and genetic aspects of endothelial dysfunction in renal patients. We will conduct a randomized, controlled, mechanistic study on the in vivo homeostasis of these metabolic pathways, and their influence on endothelial dysfunction of renal patients, and in healthy controls. The influence of dietary supplementation with arginine and folic acid on these metabolic pathways will also be explored. Relevant enzymatic genotype (MTHFR and DDAH), will be correlated with the metabolic phenotype. We hypothesize that dysregulation of the metabolism of the L-arginine-NO pathway, the methionine-homocysteine cycle and ADMA kinetics contributes to endothelial dysfunction and that arginine and folic acid supplementation will improve homeostais of these pathways. The aims are: (1) to assess NO bioavailability in CRD and ESRD patients and in healthy controls in relation to: (l.a) whole body rates of NO and arginine synthesis, methionine transmethylation, homocysteine re-methylation and transulfuration, cysteine oxidation and the rates of synthesis of whole blood glutathione, by conducting primed, constant intravenous infusions of the stable isotope tracers L4guanidino 15N2] arginine, L-2H3-methyl]methionine and L- I) 3C]methionine;L-' 3Cureido]citrulline and L-' 3C]cysteine. (l.b) The plasma concentrations of the asymmetric dimethyl arginine (ADMA) and activity of DDAH. (l.c) The differences of these metabolic parameters across the three groups. And (2) To explore the regulatory effects of a 4-week dietary supplementation with (a) arginine or (b) folic acid on the homeostasis of these pathways. The primary endpoint is NO bioavailability and the predictor variables are the kinetic parameters. State-of-the-art mass spectrometric techniques and vascular imaging will be used. The long term objective is to gain new and relevant knowledge about the mechanisms of these processes and to eventually improve the outcome of CVD in these patients.